2004-11 Trans Fat & Your Diet

Despite the challenges with regards to nutritional impact and long-term safety, food processing is a key component in providing adequate and safe food supply to a growing population. The designing of new food products is generally based on the understanding of their health and nutrient benefits at the time of product development. Current opinions on food products are often based on new research findings, which places pressure on food producers to provide alternative options. One of the best examples in this regard is the almost continually evolving debate on the impact of edible fats and oils (eg. margarine, butter, fish oils, etc) on human health, as many  research studies have shown that diets rich in saturated fats and cholesterol may increase the risk of a number of life threatening diseases in humans.

There are three different types of fat in food: saturated fat, monounsaturated fat, and polyunsaturated fat. Fats and oils of animal origin, such as butter and lard, are based entirely of saturated fats (no double bonds in the carbon chain). Fats and oils derived from plants mostly contain monounsaturated and polyunsaturated fats (one or more double bonds in the carbon chain). With the research findings that the consumption of vegetable oils (olive oil, corn oil, etc.) is heart healthy, the proportion of vegetable oils in the North American diet has progressively increased over the past thirty years. In essence, the manufacturers have been producing solid fat from vegetable oil (margarine) as a replacement for animal fat (butter).

Edible fats and oils are made by the esterification of fatty acids with glycerols. Margarine is generally produced by the hydrogenation of vegetable oils in the presence of metal catalysts and hydrogen gas. However, the processing of oil alters the fatty acid composition of the oil.  Complete hydrogenation saturates all double bonds while partial hydrogenation saturates some double bonds and converts the others from “cis” to “trans” form. Natural fatty acids generally assume a “cis” configuration, where the olefin hydrogens are located on the same side of the double bond on the fatty acid chain. As a result, these fatty acids possess a bend about 30o at the double bond making it difficult for the fatty acid chains to pack tightly and stay at liquid form at room temperature.

On the other hand, “trans” double bonds have olefin hydrogen atoms on opposite side of the double bond forming straight chain carbon chains similar to saturated fatty acids allowing compact packing of the fatty acid chains.  For example, Oleic (C18:1, cis) and Linoleic (C18:2, cis) acids are naturally present cis configured unsaturated fatty acids in vegetable oil with one and two double bonds, respectively.  Elaidic (18:1, trans) and Linolelaidic (18:2, trans) acids are “trans” isomers of the Oleic and Linoleic acid. The two former compounds possess a curved structure, while the two latter compounds possess a straight chain structure. Therefore, the more complete the hydrogenation, the firmer the oil becomes and longer the shelf life.

Partial hydrogenation of vegetable oils results in a combination of “cis” and “trans” fatty acids and a final product with semi solid consistency. Due to the straight chain structure of trans fatty acids, recent research findings have shown that the functionality of trans fat is similar to saturated fat, and may be associated with increased serum cholesterol levels exposing consumers to high risk of heart related diseases.    

In response to the above findings, the United States Food and Drug Administration (FDA) issued a regulation in July 2003 requiring the mandatory labeling of trans fat on all food products by January 2006.  In Canada, all food labels require the declaration of the amount trans fat in food.  However, some differences exist between the two countries in relation to trans fat declaration on food labels. The calculation of percent Daily Value (%DV) for saturated fat in Canadian label includes the trans fat content, while the US label does not include trans fat content. US labels allow the declaration of trans fat or saturated fat as “0” when the saturated fat or trans fat content is less than 0.5g.  In comparison, Canadian rounding rule allows the declaration of saturated and trans fat as “0” only if the product meets the “free of saturated fatty acids” and “free of trans fatty acids” claims. In all other cases, the amount has to be declared to the nearest multiple of 0.1g.

Until recently, the analysis of “total fat” in foods was conducted by extracting the samples with a combination of organic solvents such as ethanol, diethylether, and pet ether. Pre-digestion of food using acids and bases might be necessary for the removal of other interfering nutrients. The extracted solvent is evaporated and the remaining residue is used to calculate the fat. However, for the purpose of nutrition labeling, the “total fat” is defined as “all lipid fatty acids expressed as triglyceride equivalents”. 

According to the new definition, further quantification of individual fatty acids in the extracted fat is necessary by gas chromatography for the calculation of total fat in foods. For this purpose, individual fatty acids are quantified using an internal standard added at the beginning of the fat extraction. The fatty acids are then mathematically converted to their triglyceride equivalents and summed to get the total fat content. 

CANTEST is accredited by the Standards Council of Canada (SCC) for the analysis of total fat in foods as triglycerides for nutritional labeling purposes. The analysis is based on AOAC (Association of Official Analytical Chemists) 996.06 method using GC mass spectroscopy.